The present invention relates to an attachment structure for air pumps used in free axles that drive actuators in differentials having a free-axle mechanism. The actuators switch between a standard differential state and a free axle state. Differentials are used to provide smooth, automatic operation of a vehicle without slippage of the drive wheels when a rotation difference between the left and right drive wheels is required. Four-wheel drive vehicles have front differentials and rear differentials. There are also so-called "part-time" four-wheel drive vehicles that allow switching between two-wheel drive and four-wheel drive.
When part-time four-wheel drive vehicles are operated on paved roads, the transfer section switches to two-wheel drive and the vehicle is driven only by the rear wheels. In this case, the front-wheel drive chain, including the front-wheel tires, the drive shaft, the front differential, and the front propeller shaft are all driven by the rear tires. Thus, compared to regular rear-wheel drives, the load on the driven elements is large and fuel consumption is increased. In the type of two-wheel drive to which the present invention applies, the front-wheel drive chain is freed from the drive system, thus preventing loss of power. The front axle is locked to the drive system during four-wheel drive operation, and thus the drive force from the transfer is transferred to the front axle. This kind of free-axle (axle lock) mechanism is used in differentials. This allows the transfer of tire rotation to the differential to be blocked, thus reducing the load on the front differential and the front propeller shaft.
Briefly, when a free-axle mechanism is switched from two-wheel drive to four-wheel drive, shifting the transfer lever causes a synchronization mechanism, added to the front drive clutch, to forcibly synchronize engagement and provide shifting to four-wheel drive. With the activation of the 4WD switch of the transfer, the 4WD controller waits for a fixed time, e.g., one second or less, and then activates a positive-pressure air pump. The positive pressure generated by the air pump is sent to an actuator inside the front differential to lock the axle lock clutch (axle locking), thus making 4WD operation possible.
When switching from four-wheel drive to two-wheel drive, the activation of the 4WD switch of the transfer causes the release valve in the air pump to open to the atmosphere. This lowers the actuator pressure inside the front differential and frees the axle lock clutch.
Referring to FIG. 9, a prior-art free-axle air pump used to drive this type of actuator for free-axle mechanisms is generally placed in the engine compartment. FIG. 9 also shows an attachment structure for free-axle air pumps. FIG. 9 also shows the piping structure inside the bonnet, i.e. in the engine compartment, for a front differential 100 and an air pump 102 attached to a strut tower 101.
One end of a rubber hose 103 is connected to air pump 102. The other end of rubber hose 103 is connected to one end of a metal air pipe 107. Metal air pipe 107 is attached to a front wheel housing panel 104 by clamps 105 and 106. The other end of metal air pipe 107 is connected to a rubber hose 110. Rubber hose 110 emerges from a front differential 100 and extends over a cross member 108 to its connection with metal air pipe 107. An intermediate point of rubber hose 110 is clamped to cross member 108 by a clamp 109. R rubber hose 110 is long enough to accommodate the relative displacement between air pipe 107, coming from air pump 102, and front differential 100.
However, an ever-increasing number of accessories such as anti-lock brake system (ABS) actuators are being placed in the engine compartment. In particular, four-wheel drive vehicles use many accessories. Consequently, finding a location for the installation of accessories in the bonnet is often difficult. Furthermore, with a large number of accessories in the bonnet, wiring harness arrangements become complicated.